An avalanche phenomenon occurs when light is incident to an optical diode and a reverse-bias voltage is increasingly applied, thereby producing electrons that are accelerated in an electric field, further resulting in cascading atomic collisions. This avalanche produces new electrons and holes for electrical conductive use in a device. An avalanche photodiode (APD) is used for converting an optical signal into an electrical signal and as a light-receiving element in an optical communication system, which makes it highly useful in digital communications systems. Further, the APD normally includes its own gain control, which makes it effective in detecting low levels of light.
In many optical communications systems, an active avalanche photodiode (APD) gain control circuit is used in an optical receiver, which conventionally includes a bias generator for varying the bias on a variable gain APD in response to bias control values generated by a controller. APDs have gained increased consideration for use in such systems because they are capable of amplifying photocurrent internally, without the need for optical pre-amplification. It has been found that an optimized APD gain can improve the performance of optical communication systems. Furthermore, the bit error rate (BER) of an APD photo-receiver has been correlated with APD gain. In general, a logarithmic expression of BER evolves along two regimes with respect to APD bias. A first regime, in which BER drops with increasing APD bias voltage, and a second regime, where BER shows a local minimum.
Measuring BER using a programmable attenuator (ATT) and power monitor (PM) is the conventional method to set the APD operation point in laboratory test conditions, which requires human input and both ad-hoc and/or predetermined decision-making.
However, the conventional technique requires human intervention decision-dependent routines. Thus, there is an unmet need in the prior art to provide an automated mechanism for optimizing the APD optical receiver operation. Accordingly, it would be advantageous to provide an automated method and apparatus for adjusting and setting the APD operation point without human intervention.